Technical Field
The present disclosure relates to a digital protection relay, and more particularly, to a power failure monitoring device of a digital protection relay.
Description of the Related Art
A digital protection relay receives a variety of analog information (for example, a detected voltage, a detected current and the like of an electric power circuit) and a digital input from an electric power system to determine whether or not an abnormality of the electric power system occurs. The digital protection relay is a protection device of the electric power system so as to rapidly resolve an abnormality when occurring in the electric power system by controlling a circuit breaker connected to the digital protection relay to operate to a trip position (a circuit breaker position) when the abnormality is detected.
When such a digital protection relay operates, a power failure occurs so that a central processing unit of a controller, which performs an operation processing, is shut down. Consequently, when a malfunction of the digital protection relay occurs, this may cause an accident of an electric power system so that a power failure monitoring should be treated as an important subject and a countermeasure therefor may be needed.
In such a digital protection relay, a power failure monitoring device according to the related art will be described with reference to FIG. 1.
A power failure monitoring device according to the related art is configured to include an alternating current (AC) electric power input unit (hereinafter, referred to as an AC electric power input unit) 10, a direct current (DC) electric power converter (hereinafter, referred to as a DC electric power converter) 11, a voltage divider 12, and a controller 13.
The AC electric power input unit 10 may be configured with a transformer which is connected to an AC power supply, for example, such as a normal commercial AC power supply, providing a voltage in a range of 100 to 260 volts (V) to perform a voltage drop on an AC voltage provided therefrom to provide the dropped AC voltage.
Output terminals of the AC electric power input unit 10 are connected in parallel to the DC electric power converter 11 and the voltage divider 12 to provide the dropped AC voltage thereto.
The DC electric power converter 11 is configured with a rectification circuit, for example, such as a diode bridge to rectify an AC electric power from the AC electric power input unit 10 and to convert the rectified AC electric power into a DC electric power, thereby providing the controller 13 with the DC electric power as a DC power source.
The voltage divider 12 is configured with a plurality of voltage dividing resistors to divide the AC voltage from the AC electric power input unit 10 into a voltage which is a fraction of the AC voltage, thereby providing the controller 13 with the voltage as a voltage signal representing a voltage of the AC electric power.
The controller 13 may be configured with, for example, a microcomputer including a central processing unit and a memory to compare a set reference voltage value prestored in the memory with a voltage value of the voltage signal provided from the voltage divider 12.
As the comparison result, if the voltage value of the voltage signal provided from the voltage divider 12 is less than the set reference voltage value, the controller 13 determines that a power failure occurs. Thereafter, the central processing unit included in the controller 13 safely terminates an ongoing work (process) and stores data prior to the occurrence of the power failure in the memory to securely maintain information regarding a state prior to the power failure.
In the power failure monitoring device according to the related art as described above in detail, however, the set reference voltage value is a single value which has been input to be corresponded to a voltage of a single power supply in a factory upon manufacturing the digital protection relay. Therefore, when the digital protection relay to which the set reference voltage value is input is used under a circumstance at which a voltage of a power supply is changed, there may be a problem in which the power failure monitoring device according to the related art could not recognize a power failure to cause an error.